Hydraulically-actuated operating mechanism for an electric circuit breaker



Jan. 12, 1960 P. BARKAN 2,920,607

HYDRAULICALLY-ACTUATED OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Dec. 17, 1956 Imam hlllp kan, bg W His ttovnes.

Inventor:

United States Patent HYDRAULICALLY' ACTUATED i MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Philip Barkan, Lima,'Pa., assignorto General Electric Company, a corporation of New York Application December 17, 1956, Serial No'. 628,790

' 4 Claims. c1. 121-38) closing action are of a minor nature at the beginning of a closing stroke but increase'veryrapidly near the end of the stroke. To overcome these increasing opposing forces, it has been common to close the contacts of the breaker by means of-an operating linkage so designed that it provides a rnechanic'al advantage which increases as the closing stroke progresses.

When a hydraulic motor is relied upon for imparting driving forces to such a linkage, it is desirable to provide the inlet passage to the motor with a restriction which acts to moderate the rate at which driving pressure is established within the motor. The restriction acts to prevent full source pressure from being continuously maintained in the motor during the initial portion of the closing stroke whenv the opposing forces are low and, thus, acts to prevent excessive velocity of'the motor-driven linkage during this interval. By limiting the initial ve locity of the linkage, it is possible to materially decrease the severity of the impact occurring near the 'endof the closing stroke when the opposing forces suddenly become much higher.

A problem which I have discovered to be present in hydraulically-actuated mechanisms -of the above type is that the operating linkage, because of its inertia and velocity combined with its increasing mechanical advantage, has a tendency to overrun the driving part ofthe motor during an intermediate portion of the closing stroke. My investigations indicate that in certain mechanisms where the linkage and the driving part or piston, of the motor are positively coupled together, the linkage actually drives the piston ahead of the body'of liquid therebehind. In other words, the driving, or overrunning action, of the linkage moves the piston at such a high velocity that the cylinder volume behind the piston increases at a 'greater rate than the rate at which liquidcan be supplied through the restricted inlet to the motor. Under such conditions, a vacuum tends to be drawnin the cylinder space behind the piston with the resultbeing' that dissolved gases in the liquid come out of solution and form gas pockets, i.e., cavitation occurs. These cavitation-produced gas pockets are undesirable because, due to their compressibility, they can cause erratic motion and possible stalling of the linkage, especially near the end of the closing stroke when large opposing forces are abruptly encountered.

Having discovered the above problem, an abject of my invention is to prevent the occurrence of cavitation in a hydraulically-actuated operating mechanism for an electric circuit breaker.

, Another object is to incorporate into a hydraulic motor means for overcoming any tendency of a driven linkage to produce cavitation in the motor.

aerate? 1C6 Patented Jan. 12, 1969 In carrying out my invention in one form, I compensate for the overrunning action of the driven linkage by providing a compensating reservoir which communicates with the cylinder space behind the motor piston through a flow passage which is located downstream from the restriction in the motor supply line. Within this reservoir, there is provided means responsive to the liquid pressure within the cylinder space for forcing sufficient liquid from the reservoir into the cylinder space to maintain the pressure within the cylinder space above any value at Which'cavitation can occur. As a result of this action, the formation of cavitation-produced gas pockets within the cylinder space is effectively prevented despite the fact that the piston travels at such a high velocity that the cylinder volume therebehind increases at a greater rate than the rate at which liquid can be supplied through the restriction in the motor supply line.

For a better understanding of my invention, reference may be had to the following specification taken in con- :unction with theaccompanying sheet of drawing, wherein:

The single figure diagrammatically illustrates a circuit breaker operating mechanism embodying one form of my invention.

Referring now to the drawing, there is shown, in opencircuit position, a typical oil circuit breaker 10 comprising two identical pole units 11 and 12 which are adapted to be electrically-connected in series by a conductive cross-blade 14 when the breaker is closed. Each pole unit comprises a stationary interrupting contact 15 and a movable interrupting contact 16 which is biased away from the stationary contact by a suitable compression spring 17. In the open-circuit position shown, the crossblade 14 is'separated from the movable contacts 16 so as to provide a pair of isolating gaps 18 between the two pole units.

To close the breaker, the cross-blade 14 is driven upwardly through its closing stroke. Only slight opposition is encountered during the first portion of the closing stroke inasmuch as the cross-blade is merely moving through the isolating gaps 18. However, when the crossarm encounters the movable contacts 16 and begins to compress the springs 17, the opposing forces abruptly increase and continue to increase until the end of the closing stroke, at which time the contacts 15 and 16 are in circuit-closing engagement with the opening springs 17 fully charged. The magnetic forces which are established by closing the contacts further contribute to the greatly increased opposition which is encountered near the end of a closing stroke.

For transmitting closing forces to the cross-blade 14,

v a typical straight-line linkage 20 is provided. This linkage 20 comprises a reciprocable operating rod 21 rigidly connected at its lower end to the cross-blade 14 and pivotally connected at its upper'end to a lever 22. The lever 22 is pivotally mounted at 23 on a guide link 24 which, in turn, is supported on a stationary pivot 25. Pivotally connected' 'to the lever 22 in its central region is a bell-crank 2,6 which is mounted for angular movement about a stationary pivot 28. Closing forces are transmitted to the bell crank 26 through a connecting link 30 which is pivotally connected at one end to the bell-crank 26 and at its other end to another bell crank 32. This second bell crank 32 has a stationary pivot 33 about which it is driven during a closing operation by a driving link 34 pivotally connected at one end to the bell-crank 32. The other end of the driving link 34 is pivotally connected to a reciprocable driving rod 36 by a pivot pin 37.

Closing of the breaker is accomplished by driving the rod 3t: rapidly downward to pivot the bell-crank 32 in tween the sections 65 and 66 of th'esupply line.

mits pressurized liquid to flow from the accumulator 60 to V v the motor 50 to effect the above-described closing action.

direction about its pivot 23,- and this acts to drive the operating rod 21 rapidly upward to produce contact-closing. At the end of the closing stroke, the linkage Z is held in its.closed-circuit positionby a latch 40 which falls in behind the pivot "pin 37 when the drivingrod 36 nears the end of its-downward stroke. 1

To enable the contacts to be smoothly closed against the high opposing forces which are encountered near the end of the closing stroke, it is common to design the chanical advantage increases as the closing stroke progresses. To this end, it will be apparent that, in my closing linkage 20, the bell crank 32is so constructed that the moment arm between the pivot 33 and the'driving 7 link 34 increases as the closing stroke progresses. Similarly, the moment arm between the pivot 28 and the connecting link 30 increases as the closing stroke progresses,

and also the bell crank 26v moves into a toggle position with respect to lever Has the closing stroke progresses.

All of these relationships contribute to a mechanical advantage which increases as the closing stroke progresses. For actuating the driving rod 36 so as to produce the above-described closing action of the linkage "20, I provide a hydraulic motor'50. This hydraulic motor 50 comprises a cylinder 51 and a piston 52, which. is mov' able in the cylinder and is positively connected to the driving rod 36. As shown in the drawing, when the breaker is open, the piston '52 is maintained in an upper position against a shoulder 53 bymeans of alight compression spring 54. When pressurized liquid isadmitted into the cylinder space above, or behind, the piston 52, the piston is driven rapidly downward to produce the above-described closing action. Suitable vents '55 communicating with the cylinder space ahead of the piston 52 insure that no fluid will be trapped in this space to impede the downward closing motion of the piston.

Pressurized liquid is supplied to the motor from a conventional accumulator 60, which preferably contains This drives the connect- Y contact-closing linkage in such a manner that its mea pocket of highly-pressurized gasv trappedabove a sup- 7 ply of liquid contained within the accumulator. The accumulator is maintained in a charged, ,or pressurized, condition by means of a suitably-controlled pump 62 which forces liquid from a sump 63 into the accumulator 60 whenever the pressure in the accumulator falls below When the breaker is in the open position shown, the cylinder space behind the piston '52 isvented to the sump 63 by means of an exhaust passage 71' communicating with the section 66 of the supply line. When, however, the valve element 68 is lifted to establish communication between the sections '65 and 66 of the supply line for the purpose of operating the motor '50,- the passage 71 is sealed-off by means of a lower piston 72 carried by the movable valve element 68. After the closing stroke has been completed the electromagnetic control means 69 acts in 'a conventional manner to return the. valve controlling the motor 50, reference may be had to US. Patent No. 2,381,336 issued to T. R. Coggeshall and assigned to the assignee of the present invention.

Considering now a closing operation in greater detail,

if the supply line '65, 66 pern'1ited full pressure from the accumulator 360 tobe continually maintained behind the piston 52'upon opening of the control valve.67, then the motor 50, during the initial po'rtionof the stroke, would drive the linkage 20 at an extremely'highvelocity inasmuch as the opposing forces during the initial portion of the closing stroke are'very low. This extreme highvelocity tends to result in objectionably severe impacts being produced when the much greater opposing forces are abruptly encountered near the end of the closing stroke.

To reduce'this tendency toward excessive initial speed,

. the inlet passage65, is provided with a speed-governing orifice or restriction 73 which is capable of moderating the pressure build-up in the cylinder space behind the piston 52 as the piston moves through the initial portion of its stroke. The resulting lower initial speed materially lessens the. severity of the impact when the opposing forces abruptly. increase.

Preferably, the restriction 73 is located upstream from the control valve 67 so that it .does not interfere with the above-described dumping of the liquid from the space behindthe piston 52 through the valve 67 at the end of the closing stroke. Y

A problem whichI have discovered tobe'present in hydraulically-actuated mechanims of the type shown is that the operating linkage20, becauseof its inertia and ,velocity combined with its increasing mechanical advantage, hasa tendency to overrun;the driving piston 52' during an intermediate portion. of the closingstroke.

- My investigations indicate that during thisinterval, the

behind the piston 52 increases at a greater rate than the rate at which liquid can-be supplied through the orifice 73 to the cylinder 50.

Under such conditions, a vacuum tends to be drawn I in the cylinder space behind the piston'52, and this vacuum, if allowed to develop sufficiently, can cause the ilqllld in the cylinder space to emit any dissolved gases which might be present therein. The resulting gas pockets wouldbe highly undesirable because, due to their compressibility, they. could, cause erratic motion and possible stalling of the linkage20 when. the high opopsing forces are encountered near the end of the closmg stroke. 7

For overcoming this problem, I have provided the hydraulic. motor 50 with a compensator 75. This compensator comprises a cylindrical-reservoir 76' communielement 68 to its open position shown in the drawing.

This dumps or releases the pressure in the cylinder space above the piston 52 and allows the motor piston 52 to return to its upper position should the latch -40 be tripped, say by the solenoid 40a in response to a fault in the power eating with the cylinder space behind the main piston 52 by means of aflow passage 77 which is located downstream from the-orifice 73 with respect to flow into the cylinder space. A movable compensating piston 78 is provided within the reservoir 76 and is closely surrounded in sealed relationship by the cylindrical walls of the reservoir. A compression spring 79 ads to bias the compensating piston upwardly away from its seat .Stl-and into engagement with a suitable stop 81. 7

Under normal operating pressures, the fluid pressur within the main cylinder 51 forces the compensating piston 78 downwardly against its seat 80 thereby compressing the spring 79. When, however, the pressure in the main cylinder 51 falls to a predetermined safe value as a result of the previously-described high piston velocity, the spring 79 drives the compensating piston upwardly off of its seat 80. This forces liquid from the compensating, reservoir into the main cylinder 51 as such a rate as to maintain a pressure within the main cylinder which is sulficeint to prevent any tendency toward cavitation. The predetermined minimum safe value of pressure referred to above should be a pressure which is appreciably above any pressure at which cavitatlon can occur. For example, with most suitable types of 011, a pressure of about five pounds per square inch provides adequate protection against cavitation.

During a normal operation of the motor 50, leakage of pressurized liquid from the compensating reservoir 76 is effectively prevented by the coactionof piston 78 with its seat 80. In this regard, the pressurized liquid within the reservoir 76 forces the piston 78 against the seat 80 with a high force which effectively seals the reservoir against leakage past the piston. The seat '80 also desirably serves as a stop which prevents the spring 79 from being overcompressed by the high pressures within the reservoir 76.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a circuit breaker having a contact which is movable through a predetermined closing stroke, a cylinder, a piston movable therein, and means including a supply line containing a piston-speed-governing restriction for supplying pressurized liquid to the cylinder space behind said piston, a linkage positively connected to said piston and operatively connected to said contact for transmitting closing forces to said contact in response to the admission of pressurized liquid through said restriction to said cylinder space, said linkage having a mechanical advantage which increases as said closing stroke progresses and having a mass and velocity which are of such values that the linkage acts during an intermediate portion of the closing stroke to drive said piston at a velocity which increases the cylinder volume behind said piston at a higher rate than the rate at which liquid flows through said restriction into said cylinder space, a compensating reservoir communicating with said cylinder space through a flow passage which is located downstream from said restriction with respect to flow into said cylinder, and means responsive to the liquid pressure within said cylinder space for forcing sufiicient liquid from said reservoir into said cylinder space to maintain the pressure Within said cylinder space above any value at which cavitation can occur.

2. The apparatus of claim 1 in combination with control valve means located in said supply line for controlling the flow of liquid into and out of said cylinder, said restriction being located in a position which is upstream from said control valve means with respect to flow into said cylinder.

3. In a circuit breaker having a contact which is movable through a predetermined closing stroke, a cylinder, a first piston movable therein, and means including a supply line containing a piston-speed governing restriction for supplying pressurized liquid to the cylinder space behind said first piston, a linkage positively connected to said first piston and operatively connected to said contact for transmitting closing forces to said contact in response to the admission of pressurized liquid through said restriction to said cylinder space, said linkage having a mechanical advantage which increases as said closing stroke progresses and having a mass and velocity 6 which are of such values that the linkage acts during an intermediate portion of the closing stroke to drive said first piston at a velocity which increases the cylinder volume behind said first piston at a higher rate than the rate at which liquid flows through said restriction into said cylinder space, a compensating reservoir communicating with said cylinder space through a fiow passage which is located downstream from said restriction with respect to flow into said cylinder, a second piston located within said reservoir and movable in one direction to force liquid from said reservoir into said cylinder space, and biasing means responsive to the liquid pressure within said cylinder space for moving said second piston in said one direction sufficiently to maintain the pressure within said cylinder space above any value at which cavitation can occur.

4. In a circuit breaker having a contact which is movable through a predetermined closing stroke, a cylinder, a first piston movable therein, and means including a. supply line containing a piston-speed-governing restric tion for supplying pressurized liquid to the cylinder space behind said first piston, a linkage positively connected to said first piston and operatively connected to said contact for transmitting closing forces to said contact in response to the admission of pressurized liquid through said restriction to said cylinder space, said linkage having a mechanical advantage which increases as said closing stroke progresses and having a mass and velocity which are of such values that the linkage acts during an intermediate portion of the closing stroke to drive said first piston at a velocity which increases the cylinder volume behind said first piston at a higher rate than the rate at which liquid flows through said restriction into said cylinder space, a compensating reservoir communicating with said cylinder space through a flow passage which is located downstream from said restriction with respect to flow into said cylinder, a second piston located within said reservoir and having a seat against which said second piston is forced by pressure within said reservoir, said second piston acting when driven away from said seat to force liquid from said reservoir into said cylinder space, and biasing means operable upon reduction of the pressure in said reservoir to a predetermined value to drive said second piston away from said seat thereby forcing liquid into said cylinder space, said predetermined value being above any value at which cavitation can occur within said cylinder space and the amount of liquid forced by said second piston into said cylinder space being sufiicient to maintain the pressure within said cylinder space above any value at which cavitation can occur.

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